The biological functioning of some proteins is critically dependent on their state of polymerization, or self-association. Knowledge of the stoichiometry and thermodynamic properties are quite useful in forming hypotheses on the mechanism of the association. It is proposed to carry out such measurements on the self-association of protein from the tobacco mosaic virus, a process thought to resemble at least in part the assembly of the virus in the plant cell. Further we shall investigate similar self-association reactions in other systems, initially, the nucleation reaction in the self-association of flagellin, the principal protein of bacterial flagella. The approach depends heavily on equilibrium centrifugation in obtaining information on structural intermediates. Some information has already been obtained as part of the objectives of the original application as described in the research plan. It is now necessary to provide in addition to the above objectives, increased speed and efficiency of doing experiments.